1. Field of the Invention
The present invention relates to a telescopic apparatus capable of measuring the displacement or inclination of its supporting structure which may affect its pointing direction in order to correct the direction.
2. Description of the Related Art
In the field of radio astronomy, in recent years, there have been strong demands towards observing higher-frequency waves from extremely high frequency waves to submillimeter waves. When observing radio objects of a high frequency, higher accuracy is demanded of the reflector surface of a telescope and of the beam-pointing or tracking thereof. Meanwhile, in order to improve the efficiency of observation, the widening of the diameter of the telescope advances, and it is desired that the observation can be performed under any weather conditions at any time of night and day. Because of the widened diameter of the telescope, the deformation thereof caused by its weight becomes large, and moreover, the thermal deformation caused by solar radiation and the deformation caused by wind pressure also become large. As a result, it becomes difficult to obtain high pointing and tracking accuracy thereof. In order to meet the demand for such high pointing and tracking accuracy, the technology that measures the pointing error of the reflector of the telescope, and corrects the error in real time is required. The factors that cause the pointing error of the telescope include the deformation of the structural part supporting the primary reflector. As a method of measuring this deformation, an optical measuring method using laser and a photodetector for detecting the laser and a measuring method using a mechanical technique are conceived. However, for the former method, a large measurement error may be caused by fluctuations in the atmosphere in the optical system, and further, high-speed measurement may be difficult because of delays in processing the photo-detected image. On the other hand, JP-A-6-117854 discloses, as the measuring method using the mechanical technique, a method of measuring the angle of inclination of or the difference of altitude of the structure.
The apparatus disclosed by JP-A-6-117854 measures the angle of inclination of or the difference of altitude of the structure by measuring the deformation of one parallel link mechanism. However, this apparatus cannot measure the horizontal displacement and vertical displacement of the structure to be measured. For this reason, there is a problem that this mechanical technique is not suitable for a method of measuring the deformation of the reflector-supporting structure to correct the pointing error of the telescope.